Antenna assembly comprising a surface dipole

ABSTRACT

An improved antenna assembly, wherein: the opposing end regions of the dipole halves are each electrically connected to a respective connection line; the connection lines lead to two amplifiers; the outputs of both amplifiers are connected to the two inputs of a transform, whose output is at least indirectly electrically connected to a connector, a coaxial connector; one or more filters are provided; the filters are positioned between the connection lines and the connector terminal; the filter or filters is/are designed to suppress mobile radio frequency ranges and/or to protect broadcasting signals.

This application is the US national phase of international applicationPCT/EP2003/010136 filed 11 Sep. 2003 which designated the U.S. andclaims priority of DE 102 42 935.9, filed 16 Sep. 2002, the entirecontents of each of which are hereby incorporated by reference.

The invention relates to an antenna arrangement having a flat dipole, asclaimed in the precharacterizing clause of claim 1.

Dipole antennas are sufficiently well known and can be used to receivewidely differing frequencies. The length of the dipole halves in thiscase depends on the respective frequency range to be transmitted orreceived.

In this context, in principle, flat dipoles are also known whose dipolehalves comprise, for example, two rectangular conductive dipole halveswhich, for example, may be produced on a substrate, even in the form ofa printed circuit board.

Flat dipoles such as these may be used, for example, for DVB-Treception. However, on the one hand they have a Q-factor which is notsufficient for many applications and/or in particular they do not havean adequate bandwidth particularly when they are intended to be designedto be comparatively compact in comparison to the operating wavelength.

Fundamentally, it could be possible to design an antenna arrangementwith a flat dipole, by way of example, for the UHF band, that is to sayfor a frequency range which extends from about 470 MHz to 862 MHz.

If, in contrast, one wished to design a flat antenna for the VHF band,that is to say, by way of example, for a frequency range from 160 MHz to230 MHz, then antennas such as these would have to be physicallyenormously large.

An antenna arrangement of this generic type has been disclosed in DE 3405 044 C1. This comprises a flat dipole whose dipole halves are providedwith end areas which run towards one another to a point, where arespective connecting line is connected, which leads to two amplifiers.The outputs of the amplifiers are then interconnected via a transformerin the form of an addition element and are connected to a commonconnecting point, preferably in the form of a coaxial connection.

In contrast, the object of the present invention is to provide animproved antenna arrangement with a flat dipole, in particular for DVB-Toperation. In this case, the antenna according to the invention shouldbe comparatively small and should preferably be operable in twofrequency bands, specifically, by way of example, in the UHF band and inthe VHF band. However, the antenna should in this case also be suitablefor disturbance-free operation.

According to the invention, the object is achieved by the featuresspecified in claim 1. Advantageous refinements of the invention arespecified in the dependent claims.

It must be regarded as being quite surprising that the solutionaccording to the invention has for the first time made it possible todesign an antenna arrangement with a flat dipole with comparativelysmall dimensions in order to be capable of use in this case inparticular not only for the UHF range but also for the VHF range.Particularly for the last-mentioned range, it is in this case surprisingthat this can be achieved by means of a comparatively physically smallantenna.

The antenna arrangement according to the invention also comprises, as inthe case of the prior art, an active antenna with an amplifierarrangement. Each dipole half is in this case provided with a separateconnecting line, in each of which an amplifier module is arranged, atthe dipole ends which point towards one another (and are located in thecenter).

However, it was impossible to design an antenna arrangement with a flatdipole which has good reception characteristics for two such distinctfrequency bands, for example in the UHF and VHF range and which, whilebeing physically small, can be used in particular for DVB-T operation.

The antenna according to the invention in this case has characteristicswhich are as good as if it were formed from two separate individualantennas, with one of the individual antennas being optimized, forexample, to receive the VHF band and the other individual antenna beingoptimized to receive the UHF band!

The antenna according to the invention is in this case optimized forminimum noise. This is achieved by the further surprising feature thateach dipole half initially has its own associated amplifier stage. Theoutputs of the amplifier stages are then joined together, with acoplanar line, which leads to a coaxial cable connection, being used inone preferred embodiment here.

The antenna according to the invention is distinguished in that at leastone and preferably two or more filter arrangements or filter modules isor are provided, which make it possible to suppress specific frequencieswhich are a hindrance to optimum operation. Frequency bands such asthese which need to be suppressed may, for example, be radio frequencybands or else specific mobile radio frequency bands.

One preferred variant according to the present invention in this casealso provides for the connecting lines, that is to say the lines betweenthe end areas of the dipole halves and the respective downstreamamplifier, to have a capacitive coupling, that is to say, in otherwords, a capacitance. Inter alia, this also improves the electromagneticcompatibility (improved EMC protection).

One preferred development of the invention in this case also providesfor a high-pass filter also to be provided between the two dipole halvesand thus between the two inputs of the two amplifier stages. In thiscase, the high-pass filter may be electrically connected directlybetween the outputs of the dipole halves, that is to say still upstreamof the capacitances which are preferably provided and are integrated inthe connecting lines. However, this high-pass filter can also beconnected at a different point, specifically to those sections of thetwo connecting lines which are located between the two capacitances thatare provided in the connecting lines and the downstream amplifiers. Inboth cases, the capacitances which have been mentioned in the twoconnecting lines further improve the effect of the high-pass filter.

Finally, it has been found to be advantageous for the two amplifierstages to be joined together on a common output line via a transformer.A 1:1 transformer is preferably used for this purpose, for example aGuanella transformer.

A further advantageous improvement can be achieved by, for example,first of all arranging a low-pass filter (GSM filter), which may thenalso be followed by a bandstop filter, between the coaxial connection ofthe antenna arrangement and the two amplifier stages, preferably betweenthe coaxial connection and the transformer that has been mentioned. Thelow-pass filter that has been mentioned makes it possible to ensure thattelephone calls can be made without any problems in the air, that is tosay telephone calls can be made using a mobile radio or so-calledcellular telephone without the possibility of these frequencies beingreceived by the indoor antenna that has been mentioned and thecorresponding signals being able to reach the coaxial connection. Thebandstop filter which has been mentioned can preferably be in the range,for example, between 230 MHz and 470 MHz, and is used to cut off thisfrequency range which is generally kept free and is available forvarious services. This frequency band range includes control frequencieswhich can be used freely for electrical appliances, etc.

Despite the flat dipole structure, the antenna according to theinvention has a virtually optimum omnidirectional characteristic. It isparticularly suitable for indoor operation, especially for DVB-Treception of broadcast radio and television programs.

Further advantages, details and features of the invention will becomeevident in the following text from the explained exemplary embodiments.In this case, in detail:

FIG. 1 shows a schematic plan view of the antenna according to theinvention;

FIG. 2 shows a front view of the antenna parallel to the plane of thesubstrate, but omitting the coaxial cable connection and the electricalline and components which are electrically connected to the connectingpoints (which point towards one another) of the dipole halves;

FIG. 3 shows an enlarged plan view of the amplifier arrangement andconnecting arrangement, via which the dipole halves are connected to acoaxial connection;

FIG. 4 shows an embodiment of the invention, slightly modified from thatshown in FIG. 3, with additional capacitances in the two connectinglines which originate from the dipole halves; and

FIG. 5 shows an embodiment which has once again been slightly modifiedfrom that shown in FIG. 4, in which the high-pass filter is connectedbetween the two connecting lines, but downstream from the capacitancesrather than upstream of them.

FIG. 1 shows a schematic plan view of a first exemplary embodiment of anantenna arrangement according to the invention in the form of a flatdipole 1 with two dipole halves 1′ which extend in the longitudinaldirection 3.

The flat dipole 1 has conductive flat elements 5 for the dipole halves1′, which can preferably be formed on a substrate 7, in particular inthe form of a printed circuit board 7′.

On the basis of the exemplary embodiment shown in FIGS. 1 and 2, theactual dipole halves 1′ are designed to be triangular and are alignedsuch that their tips point towards one another. The dipole halves 1′ inthis case have a length L and a width B on their base on the plane E onwhich the dipole halves 1′ extend.

The two feed points 11 a and 11 b for feeding the respective dipole half1′ are provided at the two inner ends 9 (which point towards oneanother) of the dipole halves 1′ (FIG. 3).

In the illustrated exemplary embodiment, so-called roof capacitances 1″are formed at the opposite, that is to say outer, ends 13 of the dipolehalves 1′ in order to widen the bandwidth and/or to improve the Q factorof the antenna, which roof capacitances, in the illustrated exemplaryembodiment, intrinsically have a rectangular structure and in theprocess run at right angles to the longitudinal extent 3 of the flatdipole 1. The projections 16 of the roof capacitances 1″, that is to saythe extent to which the roof capacitances 1″ overhang the side boundaryedges 17 of the dipole halves 1′, may be chosen differently, foroptimization. In the illustrated exemplary embodiment, these overhangs16 are on the one hand each provided on only one side (specifically onthe same side as the dipole halves 1′) and on the other hand are smallerthan the longitudinal size of the dipole halves 1′ without the roofcapacitances 1″. On the other hand, the overhangs have an extent in thetransverse direction with respect to the longitudinal direction of theflat dipole 1 which is greater than 10%, and is preferably greater than20%, being about 20% to 60% in the illustrated exemplary embodiment, andin particular corresponding to about 40% of the longitudinal extent ofone dipole half 1′. The width of the roof capacitances 1″ in theillustrated exemplary embodiment is kept comparatively narrow and ispreferably less than 20%, in particular less than 10% or even less than5% of the length L of one dipole half.

The exemplary embodiment illustrated in FIGS. 1 and 2 also shows thatthe dipole halves 1″ are preferably arranged symmetrically with respectto a transverse plane of symmetry 27.

In the exemplary embodiment illustrated in FIG. 1, these dipole halves1′ are designed such that they become continuously broader from theinside towards their outer end, so that their side boundary edges 17 runin a divergent form from the inside to the outside. The angle at whichthe side boundary edges 17 diverge with respect to each dipole half 1′may, for example, be around 30°. Preferred values are 10° to 50°, and inparticular 20° to 40°. This therefore results in the dipole halves 1′having a triangular or trapezoidal structure when seen from above. Theroof capacitances 1″ are likewise once again preferably provided at theouter end and then possibly project only to a minor extent beyond theouter broad end of the dipole halves 1′ at the sides. However, incontrast to the exemplary embodiment shown in FIG. 1, other dipole halfshapes are also possible. For example, there is no need for the innertips 9, which point towards one another, so that the shape would be moretrapezoidal, with approximately straight boundary edges being formedinstead of this on one another on the inside. Furthermore, the boundaryedges 17 of the dipole halves also do not need to run in a straightline. In fact, if required, they can also change two or more times froma highly divergent angle to a less divergent angle.

Finally, it is even feasible for the dipole halves 1′ to be providedwith a rectangular structure so that two rectangular flat elements 5,which are arranged alongside one another in the longitudinal direction3, are used as dipole halves. This illustrates the fact that, inprinciple, widely differing shapes are possible for the dipole halves1′, with the chosen triangular to trapezoidal shape being used bypreference.

FIG. 3 likewise shows that two amplifier stages, and a coplanarconnecting line, which leads to a coaxial cable connection, are providedfollowing the plane of symmetry 27 approximately symmetrically in alongitudinally extending area, as will be described in the followingtext with reference to FIG. 3.

The two dipole halves 1′ are illustrated partially, in a schematic form,once again in FIG. 3 and are triangular in the exemplary embodimentshown in FIG. 1, with their tips being aligned such that they runtowards one another symmetrically with respect to the vertical plane ofsymmetry 27.

The feed point 11 a and 11 b, respectively, is then located precisely atthe extreme front point 9, of each of the two dipole halves 1′, that isto say at the points which are in each case closest to one another,which feed points 11 a and 11 b are connected to one another viaconnecting lines 49 a and 49 b as well as a connection line 51, to beprecise with a high-pass filter 52 connected between them. Thishigh-pass filter is used to protect the amplifier inputs in particularagainst powerful VHF transmitters (87 MHz to 108 MHz) and against otherradio services in particular below 160 MHz.

The signal which is received via the two dipole halves 1′ is suppliedvia the connecting line 49 a or 49 b, respectively, to a respectiveseparate amplifier stage 53 a or 53 b (which stages are associated withthe individual dipole halves 1′) via the connecting lines 49 a and 49 b.In order to ensure an embodiment of the antenna arrangement with as lownoise as possible, the end areas 9 (which point towards one another) ofthe dipole halves 1′ are each electrically connected as directly aspossible to a respective amplifier 53 a, 53 b. This connection can bemade via connecting lines 49 a and 49 b which are as short as possible.The length of these connecting lines should preferably be in the rangefrom 0.2 cm to 3 cm, in particular between 0.5 cm and 1.5 cm.Alternatively, it is also possible to provide a link between the endareas 9 of the dipole halves 1′ and the inputs of the amplifiers 53 aand 53 b via a capacitance. This capacitance can be based on the use ofa discrete component. However, alternatively, it is also possible forthe capacitance to be in printed form on the substrate (printed circuitboard).

The outputs of the two amplifier stages 53 a, 53 b are then supplied tothe two inputs of a transformer 55, which is preferably a 1:1transformer (for example a so-called Guanella transformer).

The output of the transformer 55 is then connected in series to alow-pass filter 57 (a so-called GSM filter for suppression offrequencies which are used in the cellular telephone radio band) and adownstream bandstop filter, that is to say a bandstop filter 59, whichis then electrically connected to a coaxial connection 61. The low-passfilter 57 is used in particular to suppress mobile radio frequencybands, in particular the GSM frequencies. In contrast, the object of thebandstop filter 59 is to suppress the range between the two bands, thatis to say in the illustrated exemplary embodiment preferably the rangebetween 230 MHz and 470 MHz. It should be noted, just for the sake ofcompleteness, that, in principle, the low-pass filter 57 and thebandstop filter 59 can also be connected in the opposite sequencebetween the transformer 55 and the coaxial connecting point 61, incontrast to the illustration shown in FIG. 3.

The transmission path from the dipole halves 1′ to the transformer 55 isthus approximately balanced. The impedance is a function of thefrequency. The impedance on the transmission path from the output of thetransformer to the coaxial feed point 61 is preferably 75 ohms, with thecoplanar transmission path being unbalanced.

The entire arrangement is accommodated in a rectangular area 63, whichextends approximately along the plane of symmetry, on the mount, thesubstrate or the board 63. The two dipole halves 1′ can be formedtogether with the line sections of the amplifier and transmission stagein the area 63 on the same side with respect to the substrate, theprinted circuit board, etc. The amplifier stage with its line sectionsmay, however, also be formed on the opposite side of the substrate, thatis to say opposite the correspondingly conductive flat sections of thedipole halves.

The substrate 7 itself may be composed of various materials, for exampleplastic material, comparable conventional printed circuit boards, orelse from materials such as cardboard, paper etc. which are even simplerand cost even less than these.

The antenna, which is intended for DVB-T reception, may, for example, beused for VHF and UHF reception. In this case, it is extremely compactand has a length transversely with respect to the plane of symmetry 27of, for example, less than 30 cm, and possibly of even less than 20 cm,for example of 15 cm. The transverse extent parallel to the plane ofsymmetry 27 may be even less.

If the antenna as illustrated in FIG. 1 is installed with its edgelocated at the bottom in FIG. 1 on a horizontal surface, then it issuitable for reception of horizontally polarized signals. If, incontrast, it is installed rotated through 90° with respect to FIG. 1,that is to say parallel to its outer base edge of the dipole profilehalves, then it is suitable for reception of vertically polarizedsignals.

The following text refers to FIG. 4.

FIG. 4 shows an exemplary embodiment which has been modified onlyslightly from that shown in FIGS. 1 to 3. In the exemplary embodimentshown in FIG. 4, the two dipole halves 1′ do not run towards one anotherat a point but, in principle, are shown as being rectangular. Ingeneral, the dipole halves may have any suitable shape, for example aplan view with an n-sided polygonal shape.

In the same way as in the exemplary embodiment shown in FIGS. 1 to 3,the exemplary embodiment shown in FIG. 4 has connecting lines 49 a and49 b which start from the connecting points 11 a and 11 b and lead tothe inputs of the respective amplifiers 53 a and 53 b in the respectiveconnecting line 49 a or 49 b. In this exemplary embodiment as well, thetwo amplifiers 53 a and 53 b are once again connected to the two inputsof a transformer 55, whose common output is connected via a low-passfilter 57, for example a GSM filter and a downstream bandstop filter 59,to a connecting point 61, preferably a coaxial connecting point 61.

In this exemplary embodiment, the two dipole halves 1′ are likewise onceagain connected to one another via a high-pass filter 52.

Now, as an addition to the previous exemplary embodiment, the exemplaryembodiment shown in FIG. 4 also has a capacitive coupling 71 a or 71 b,respectively, in each connecting line 49 a or 49 b, that is to say ingeneral has a respective capacitance 71 a or 71 b connected in between(for example in each case in the form of a capacitor).

The high-pass filter 52 shown in FIG. 4 is connected upstream of thecapacitances 71 a and 71 b, between the two connecting lines 49 a and 49b.

This additionally mentioned capacitance 71 a or 71 b is also provided inthe exemplary embodiment shown in FIG. 5. In this exemplary embodiment,the high-pass filter 52 is likewise once again connected between the twoconnecting lines 49 a and 49 b. The only difference from FIG. 4 is thatthe high-pass filter 52 in this exemplary embodiment as shown in FIG. 5is in each case connected in that path section of the connecting lines49 a and 49 b, respectively, which is located between the output of therespectively associated capacitance 71 a and the input of the downstreamamplifier 49 a or, respectively, the output of the capacitance 71 b andthe input of the downstream amplifier 53 b. This is just intended toindicate that the high-pass filter 52 can be connected at differentpoints between the two connecting lines 49 a and 49 b.

It can thus be seen from the exemplary embodiments shown in FIGS. 4 and5 that an improvement is achieved by the connecting lines 49 a, 49 beach having at least one capacitance and/or the end areas 9 of thedipole halves 1′ being connected to the respective downstream amplifier53 a, 53 b via a capacitive coupling (capacitance).

1. An antenna arrangement having a flat dipole which is arranged on asubstrate, comprising: dipole halves including end areas, the end areaswhich point towards one another each being electrically connected torespective connecting line, plural amplifiers, the connecting linesleading to said plural amplifiers, a transformer; the plural amplifiershaving outputs, the outputs of the plural amplifiers being connected tothe two inputs of the transformer, the output of the transformer beingat least indirectly electrically connected to a coaxial connectionpoint, plural filters, the dipole halves being arranged on the substratetogether with the plural amplifiers and the plural filters, the pluralfilters being arranged between the connecting lines which lead to thedipole halves, and the connection point, the filters being provided forsuppression of mobile radio frequency ranges and/or as protection forbroadcast radio signals, a low-pass filter connected between the outputsof the plural amplifiers and the connection point in order to suppressmobile radio frequencies (cellular telephone frequencies), and abandstop filter connected between the outputs of the plural amplifiersand the connection point.
 2. The antenna arrangement as claimed in claim1, wherein the bandstop filter is connected downstream from the low-passfilter.
 3. The antenna arrangement as claimed in claim 1, wherein theconnecting lines are connected to one another via a connection line,with a high-pass filter connected between them.
 4. The antennaarrangement as claimed in claim 1, wherein the connecting linesrespectively have at least one capacitance, and/or the end areas of thedipole halves are preferably connected to the respective downstreamamplifier via a capacitive coupling.
 5. The antenna arrangement asclaimed in claim 1, wherein the low-pass filter and/or the bandstopfilter are/is provided downstream from the transformer and upstream ofthe connecting point.